129,710 research outputs found
A method to find unstable periodic orbits for the diamagnetic Kepler Problem
A method to determine the admissibility of symbolic sequences and to find the
unstable periodic orbits corresponding to allowed symbolic sequences for the
diamagnetic Kepler problem is proposed by using the ordering of stable and
unstable manifolds. By investigating the unstable periodic orbits up to length
6, a one to one correspondence between the unstable periodic orbits and their
corresponding symbolic sequences is shown under the system symmetry
decomposition
Giant isotope effect and spin state transition induced by oxygen isotope exchange in (
We systematically investigate effect of oxygen isotope in
which shows a crossover with x from
ferromagnetic metal to the insulator with spin-state transition. A striking
feature is that effect of oxygen isotope on the ferromagnetic transition is
negligible in the metallic phase, while replacing with leads
to a giant up-shift of the spin-state transition temperature () in the
insulating phase, especially shifts from 36 to 54 K with isotope
component for the sample with x=0.175. A metal-insulator
transition is induced by oxygen isotope exchange in the sample x=0.172 being
close to the insulating phase. The contrasting behaviors observed in the two
phases can be well explained by occurrence of static Jahn-Teller distortions in
the insulating phase, while absence of them in the metallic phase.Comment: 4 pages, 5 figure
Direct diffusion through interpenetrating networks: Oxygen in titanium
How impurity atoms move through a crystal is a fundamental and recurrent
question in materials. The previous understanding of oxygen diffusion in
titanium relied on interstitial lattice sites that were recently found to be
unstable, making the diffusion pathways for oxygen unknown. Using
first-principles quantum-mechanical methods, we find three oxygen interstitial
sites in titanium, and quantify the multiple interpenetrating networks for
oxygen diffusion. Surprisingly, no single transition dominates, but all
contribute to diffusion.Comment: 10 pages, 3 figures; additional supporting materia
X-Ray Flares from Postmerger Millisecond Pulsars
Recent observations support the suggestion that short-duration gamma-ray
bursts are produced by compact star mergers. The X-ray flares discovered in two
short gamma-ray bursts last much longer than the previously proposed postmerger
energy release time scales. Here we show that they can be produced by
differentially rotating, millisecond pulsars after the mergers of binary
neutron stars. The differential rotation leads to windup of interior poloidal
magnetic fields and the resulting toroidal fields are strong enough to float up
and break through the stellar surface. Magnetic reconnection--driven explosive
events then occur, leading to multiple X-ray flares minutes after the original
gamma-ray burst.Comment: 10 pages, published in Scienc
Accretion column eclipses in the X-ray pulsars GX 1+4 and RX J0812.4-3114
Sharp dips observed in the pulse profiles of three X-ray pulsars (GX 1+4, RX
J0812.4-3114 and A 0535+26) have previously been suggested to arise from
partial eclipses of the emission region by the accretion column occurring once
each rotation period. We present pulse-phase spectroscopy from Rossi X-ray
Timing Explorer satellite observations of GX 1+4 and RX J0812.4-3114 which for
the first time confirms this interpretation. The dip phase corresponds to the
closest approach of the column axis to the line of sight, and the additional
optical depth for photons escaping from the column in this direction gives rise
to both the decrease in flux and increase in the fitted optical depth measured
at this phase. Analysis of the arrival time of individual dips in GX~1+4
provides the first measurement of azimuthal wandering of a neutron star
accretion column. The column longitude varies stochastically with standard
deviation 2-6 degrees depending on the source luminosity. Measurements of the
phase width of the dip both from mean pulse profiles and individual eclipses
demonstrates that the dip width is proportional to the flux. The variation is
consistent with that expected if the azimuthal extent of the accretion column
depends only upon the Keplerian velocity at the inner disc radius, which varies
as a consequence of the accretion rate Mdot.Comment: 7 pages, 5 figures, accepted by MNRAS. Included reference
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